Not quite a throttle it seems Shane, but power on demand is possible. The following post by member andrewelectricbike tells you how to get push-button power when you want it without pedalling:
Power on demand post
However, if that doesn't suit, the Giant Suede was sold in the USA with a throttle fitted so the controller may have other connections for that.
You may get some information from one of the US agents who sold the Suede when it was current, here's one you could mail:
info@electricbikes.org
electric bikes
28725 Parkway Place
Anaheim, CA 92807
If not, try Giant in the UK, here's the contact webpage for you:
Giant customer inquiries
.